(17) Kant, J. A., J. Chem. Phys., 41, 1872 (1964). (18) Kelley, K. K., "Contributions to the Data on Theoretical Metallurgy; X I I I . High Temperature Heat Content, Heat Capacity, and Entropy Data for the Elements and Inorganic Compounds," Bulletin 584, Bureau of Mines. Washington, D.C., 1960. (19) Kellogg, H. H., J. Chem. Eng. Data, 14,41 (1969). (20) Kieffer, L. J., Dunn, G. W., Rev. Mod. Phys., 38, 1 (1966). (21) King, E.G., J. Amer. Chem. SOC.,79,2399 (1957). (22) Langmuir, I., Jones, H. A., MacKay. G. M. J., Phys. Rev., 30, 26 (1927). (23) Langmuir, I., "The Collected Works of Irving Langmuir," Vol 9, p 3, Pergamon, New York, N.Y., 1916. (24) Mallet, L., Rosen, 9.. Bull. SOC.Roy. Sci., Liege, 14,382 (1945). (25) Mandel, John, "The Statistical Analysis of Experimental Data," Chap. 5, Interscience, New York, N.Y., 1964. (26) Mandel, John, Paule, R . C., Anal. Chem., 42, 1194 (1970). (27) Moore, C. E., Nat. Bur. Stand., Circular No. 467, 1959. (28) Morris, J. P., Zellars, G. R., Payne, S. L., Kipp, R. L., "Vapor Pressure Of Liquid Iron and Liquid Nickel," U.S. Bureau of Mines, Report No. 5364, 1957. (29) Nesmeyanov, An. N., Tik-Mang, Teh, Dokl. Akad. Nauk SSSR, 116, 230 (1957). (30) Nesmeyanov, An. N., Tik-Mang, Teh, lzv. Akad. Nauk SSR, Otd. rekh. Nauk ( l ) ,75 (1960). (31) Nesmeyanov, An. N., "Vapor Pressure of the Elements," J. I. Carasso, Transl., p 396, Infosearch, London, England, 1963.
(32) Oetvos, J. W., Stevenson, D. P., J. Amer. Chem. SOC., 78, 546 (1956). (33) Paule, R. C., Mandel, John, "Analysis of lnterlaboratory Measurements on the Vapor Pressures of Cadmium and Silver," NBS Spec. Publ. 260-21, Nat. Bur. Stand., Washington, D.C.. 1971 (34) Pauling, L., "Nature of the Chemical Bond," (a) p 62, (b) p 256, Cornell Univ. Press, Ithaca, N.Y., 1960. (35) Rovner, L. H., Norman, J. H., J. Chem. Phys., 52,2496 (1970). (36) Rutner. Emile. Haury, G. L., "The Vapor Pressure and Heats of Vaporization of Nickel," Tech. Report AFML-TR-72-217, Air Force Materials Lab, Wright-Patterson AFB. Ohio, 1972. (37) Stull. D. R., Sinke, G. C., "Thermodynamic Properties of the Elements," American Chemical Society, Washington, D.C., 1956. (38) Trivedi, Hrishikesha, Proc. Nat. Acad. Sci., India, 4, 27 (1935). (39) Wang, K. L., Brody. M. D., Crawford, C. K.. Air Force Materials Lab, Report AFML-TR-69-5, Jan. 1969. (40) Weast, R. C., Ed.. "Handbook of Chemistry and Physics," 47th ed., Chemical Rubber Co., Cleveland, Ohio, 1966. (41) Wickes, C. E., Block, F. E., "Thermodynamic Properties of 65 Elements, Their Oxides. Halides, Carbides, and Nitrides," Bulletin 605, Bureau of Mines..Washinaton. D.C.. 1963. (42) Yamashito, Jiro, Masa, Kojlma, J. Phys. SOC., Japan, 7 (3), 261 (1952). Received for review May 14, 1973. Accepted September 27, 1973.
Liquid and Vapor Densities of Aluminum Bromide David S. Olson, Fred C. Kibler, Jr., David W. Seegmiller, Armand A. Fannin, Jr.? and Lowell A. King' Frank J. Seiler Research Laboratory (Air Force Systems Command) and Department of Chemistry, United States A i r Force Academy, Colo. 80840
The orthobaric liquid and vapor densities of aluminum bromide were measured from 92" to 319°C.The method simultaneously yielded the liquid and vapor densities for each (arbitrary) experimental temperature. The experimental precision was f0.0025 g/cm3, which corresponds to 0.1 % of the liquid densities, and ranged from 6 to 100% of the vapor densities over the temperature range covered. A single empirical equation was derived which was symmetrical about the rectilinear diameter and which represented both liquid and vapor densities.
As part of a program for the investigation of certain low-melting, molten salt electrolytes for high energy density batteries, we needed to know the densities of aluminum bromide liquid and vapor. Many of the physical properties of aluminum bromide have been collected in a review by Boston (2). Biltz and Voight ( 7 ) earlier had measured a few liquid densities from 100" to 265"C, Zhuravlev (70) measured liquid densities from 170" to 450°C, and Johnson et al. ( 4 ) determined liquid and vapor densities in the temperature ranges 101-490°C and 270488OC, respectively. We were interested primarily in the densities near the melting point, which was reported to be 97.5"C (9). Experimental
Aluminum bromide was synthesized by dropping Mallinckrodt analytical reagent Brz onto J. T. Baker purified granular aluminum contained in a flask in which a slight positive pressure of dry Ar was maintained. After the synthesis was complete, AIBr3 was distilled out of the reaction flask into a clean container. The distillate crystals were transferred (inside a glove box) to an ampul which
' To whom correspondence should be addressed
was then evacuated and sealed, and a further purification carried out by growing crystals from the vapor phase. This latter process was done in a manner analogous to the method we formerly used for AIC13 ( 8 ) . Orthobaric liquid and vapor densities were simultaneously determined from 363 measurements made substantially as we reported earlier for our work with aluminum chloride (5, 7 ) . Thirteen sealed borosilicate glass dilatometric tubes were used. These each consisted of two bulbs connected by a calibrated, graduated capillary. The tubes were held vertically, such that liquid AlBr3 filled the lower bulb and extended into the graduated capillary. The upper part of the capillary and the upper bulb contained AIBr3 vapor. The filled bulbs were immersed in a molten salt bath, and at each different temperature the distance from the bottom of the AIBr3 meniscus to an arrow etched on the capillary was measured with the aid of a cathetometer. From this measurement and the tube calibration data, the liquid volume was calculated. The dilatometric tubes were identical in general size and design to those described in ref. 5. They were calibrated in the same manner employed for tubes A, B, C, and D of that report. Meniscus corrections and thermal expansion corrections, the molten salt bath, and the bath temperature control were also as described therin. Bath temperature was determined by measuring the resistance of a 4-wire platinum resistance element (Electric Thermometers Trinity, Inc., Bridgeport, Conn. 06604) (100 fl nominal) calibrated against the platinum Air Force Reference Standard Thermometer which we used earlier (7). Tube calibration data are given in Tables I and I I . The distances from AIBr3 menisci to the arrows etched on the capillaries are shown in Table I l l . Without using unduly large capillaries (or small bulbs), it was not possible for a single tube to span the entire temperature range of interest. We divided the 13 tubes into five groups covering Journal of Chemical and ,Engineering Data, Vol. 19, No. 1, 1974
27
overlapping temperature ranges. The data in Table I I I were not all taken in the order listed; measurements were made with both ascending and descending temperature.
Results At a given temperature, liquid and vapor densities are related to the tube parameters and mass of AIBr3 by the set of equations DVi
+ d ( T i - V i ) - mi = 0
(1)
According to the law of the rectilinear diameter, the mean of the orthobaric densities of a substance is a linear function of temperature; that is,
In other words, the liquid and saturated vapor densities
of a substance should describe a symmetrical function about the rectilinear diameter. We assumed the liquid and vapor densities of AIBr3 were related to temperature by the equation T
+ a2Q2 + a3Q3 = 0
(3)
where Q = D - p m - -Pm-d
(4)
From Equations 1, 2, and 4, it is possible to derive the equation Qtube
=
Pm - P
(5)
~
1-24 Table I . Calibration of Density Tubes: T and m
Tube identifier
Total enclosed vol, cma (25'C)
Mass of AIBra in tube, g
A1 BI
79.17a 108.47 55.30 31.28 26.11 81.64 36.54 56.96 80.31 56.14 31.65 26.72 84.56
27.797b 34.943 28.273 25.701 29,967 25.510 24.329 22.835 24.141 25.146 22.828 26.747 29.50
CI DI El A2
D2 F2 A3 c3 D3 E3 G3
estimated uncertainty in T = i0.05 cm3.6Estimated uncertainty in m = &0.003 gram. Table I I . Calibration of Density Tubes: Fixed Parameters
Letter ot tube Vol to arrow, cm3 identifier (25OC) A B C D
E F G
28
10.478f 0.001 13.8127i 0.0006 10.898&.0.003 10.018f 0.002 11.7297 ?C 0.0007 9.468& 0.001 12.798 f 0.004
Vol of capillary,
cm3/cm (25OC)
0.0653i 0.0006 0.0610i 0.0004 0.066f 0.002 0.0662i 0.0009 0.0665f 0.0004 0.0669 i 0.0004 0.066f 0.001
Journal of Chemical and .fngineering Data, Vol. 19, No. 1 , 1974
Table 111. Experimental Measurements Height of meniscus height of etched arrow, cm5
-
Temp,
Tube
Tube
"C
A1
BI
91.89b 96.99 102.21 107.32 112.57 117.78 122.98 128.19 133.39 138.63 143.93 149.24 154.53 157.49 158.49 159.82 160.04 161.04 162.32 165.04 165.18 166.17 168.97 169.99 170.63 171.31 172.79 175.00 175.99 179.64 179.99 180.13 181.31 182.66 182.68 184.07 185.19 185.34 186.72 186.80 188.11
-1.230 -0.515 0.175 0.895 1.580 2.300 3.045 3.745 4.495 5.185
CI
93.12 98.28 103.40 106.04 108.67 111.27 113.87 116.45 120.18 121.81 124.40 126.96 129.61 132.15 134.78 136.18 137.47 138.84 140.16 141.45 142.80 144.09
-4.485 -4.080 -3.170 -2.715 -2.465 -2.065 -1.580 -1.285 -0.630 -0.500 0.285 0.720 1.055 1.435 1.625 1,810
1,990 2.215 2.395 2.610 2.775
Tube
-3.595 -2,590 -1.380 -0.340 0.110 0.200 0.535 0.470 0.700 0.875 1.360 1.520 1.555 2.105 2.395 2.550 2.620 2.865 3.260 3.475 4.155 3.530 4.280 3.855 4.080 4.575 4.460 5.140 4.715 5.335 5.050 5.365 DI
-4.695 -4.015 -3.665 -4.095 -3.690 -3.230 -2.740 -1.820 -1.615 -1.270 -0.910 -0.550 -0.115 0,255 0.435 0.620 0.795 0.980 1.170 1.370 1.555
El
-5.285 -4.780 -4.315 -3.930 -3.485 -2.900 -2.665 -2.220 -1,850 -1.420 -0,995 -0.580 -0.375 -0.185 0.005 0.260 0.480 0.725 0.905 (Continued)
Table 111. Continued Height of meniscus-height
of etched arrow, cma
Temp, O C
145.46 146.71 148.08 149.36 150.28 152.96 153.92 155.01 155.14 155.72 155.78 156.92 157.61 158.28 158.28 158.57 158.78 159.45 159.85 161.15 163.20 163.90
Tube
CI 2.990 3.195 3.350 3.580 3.675 4.145 4.520 4.545 4.725 4.810 4.520 4.990 5.110
4.900
A2
165.77 171.33 175.94 176.10 178.50 182.22 182.33 183.73 185.38 188.26 192.26 195.67 197.34 200.66 203.32 205.57 208.19 209.36 210.78 213.26 215.64 215.74 218.23 220.69 221.08 223.13 225.66 228.02 229.24 230.08 230.38 231.10 231.12 224.99 229.53 229.90 230.55 232.39 233.16
Tube
Tube
DI
El
1.770 1.955 2.120 2.325 2.450 2.855 2.870 3.130 3.210 3.130 3.370 3.475 3.575 3.580 3.535 3.650 3.740 3.770 3.920 4.265 4.340 F2
1.115 1.335 1.545 1.795 1.925 2.370 2.600 2.525 2.830 2,925 2.805 3.130 3.235 3.370 3.360 3.295 3.455 3.570 3.640 3.755 4.195 4.200 D2
-4.225 -3.540 -2.910 -2.845 -2.640 -2.150 -1.905 -1.780 -1.555 -1.395 -0.740 -0.440 -0.375 0.170 0.475 0.725 0.995 1.075 1.305 1.590 1.915 1.860 2.095 2.355 2.485 2.620 2.885 3.115 3.085 3.310 3.515 3.540 3.540
-5.150 -4.465 -3.810 -3.995 -3.845 -3.375 -3.150 -2.975 -2.780 -2.675 -1.980 -1.825 -1.670 -1.280 -0.975 -0.730 -0.455 -0.315 -0.165 0.110 0.460 0.380 0.635 0.940 1.205 1.185 1.470 1.825 2.360 2.075 2.375 2.730 2.665
-3.930 -3.210 -2.540 -2.535 -2.395 -1.690 -1.635 -1.455 -1.225 -0.860 -0.275 0.175 0.190 0.860 1.230 1.540 1* 900 1.895 2.260 2.590 2.905 2.940 3.245 3,640 3.505 3.980 4.310 4.640 4.785 4.960 4.965 5.050 5.100
A3
D3
E3
-4.665
-4.865
-5.435 -5.195 -5.180 -5.110 -5.010 -5.200
-4.505 -4.220
-4.725 -4.355
Temp, "C
Tube A3
234.70 236.53 237.70 239.73 240.31 243.81 245.24 247.10 248.24 249.06 249.07 249.30 250.17 253.34 254.62 255.13 258.40 259.68 264.48 264.54 264.87 269.48 269.59 269.59 269.59 269.65 269.66 269.67 269.69 269.73 269.86 273.15 274.77 279.71 282.82 284.25 288.75 289.00 293.63 294.28 305.68 317.64 329.03 244.19 249.11 254.73 257.80 261.44 264.81 268.44 277.28 282.04 287.28 292.04 296.63 301.71 308.90 318.75
-4.845 -4.080 -4.815 -4.350 -3.795 -4.125 -3.630 -3.830 -3.805 -3.805 -3.805 -3.750 -3.100 -3.565 -3.575 -2.780 -3.080 -2.750 -2.740 -2.775 -2.390 -2.905 -2.305 -2.900 -2.920 -2.685 -2.460 -2.725 -2.630 -2.555 -2.200 -2.395 -2.090 -1.950 -2.225 -2.080 -2.525 -1.890 -2.055 -2.260 -2.620 -3.525 -4.405
Tube D3
Tube E3
-3.915
-3.960
-3.145
-3.035
-2.690
-2.385
-1.905
-1.430
-1.350
-0.730
-0.665
0.160
0.150
1.230
1.330
2.815
2.625
4.595
4.170
c3
G3
-2.475 -1,740 -1.125 -0,855 -0.380 -0.100 0.375 1.335 1.640 1.965 2,355 2.680 2.975 3.420 3.710
-5.395 -4.480 -3.670 -3.660 -3.155 -2.990 -2.550 -1.855 -1.845 -1.530 -1.345 -1.170
-1.015 -0.390 0.150
"Total estimated uncertainty in distance from meniscus to arrow = ~ t 0 . 0 0 5cm. *Estimated uncertainty in temperature = f0.05"C. Journal of Chemical and Engineering Data, Vol. 19, No. 1, 1974
29
where rn p=-and+=T
V T
Equation 5 is a function of the cathetometer measurements and the tube calibration data. The value of Q t u k can be calculated for each tube at each temperature from the adjustable constants a. and p c and the data from Tables 1-1 I I. Equation 3 is cubic in Q. For the particular values of a2 and a3 which best represent our data, Equation 3 has two imaginary roots and one real root. The real root is Qeqn
= \-(A
+ [(2A +
+
87) {-(A -t87)
- [(2 A
8T)8T]”21’/3
+
-
4- B T ) ~ T ] ’ / ~ ~ ’ / ~ (6)
where 3
) : ( =A
Equations 3 or 10 can be solved to yield vapor density over the entire experimental temperature region; however, the estimated error becomes larger than the actual AIBr3 vapor density at low temperatures. One result of this is that the equation predicts vapor densities which increase as the temperature falls below approximately 165°C. The calculated densities all fall within the range of experimental scatter down to the lowest temperature reached, 92°C; nevertheless, this clearly is an unsatisfactory situation. Several other functions were fit instead of Equation 3, including the form we used with AIC13 (7) and the modified Guggenheim equation previously used with AIBr3 ( 4 ) . Without exception, all of these equations even more poorly represented the vapor density-temperature behavior at low temperatures. Accordingly, we decided to represent the low-temperature vapor densities by the polynomial in T
1
(9)
andB=
Equation 6 is a function of the adjustable constants a2 and a3 and i’ not directly dependent On the data Of Tables 1-111. A least-squares fit was made of the function
zi = Qeqn,t -
Qtube,i
(7)
for the values of adjustable constants all, a2, a3, and p c which minimized the sum n
i= 1
All the experimental points represented in Table Ill were given equal weights in the least-squares calculations, The standard deviation is in Q and is defined by
The selected polynomial was to be monotonic over its entire range of use. In addition, the following four constraints were applied: The density and slope calculated from Equation 9 were required to match the density and slope calculated from Equation 10 at their point of intersection. Also, the density and slope calculated from Equation 9 were required to match the density and slope at the melting point, 97.5’C, as calculated from the ideal gas law and the vapor-pressure data of Fischer et al. (3). (These values are dmelting point = 9.46 X g/cm3 g/cm3 deg). and (ad/dt)melting point = 4.59 X The lowest convenient intersection temperature (to the nearest even number of degrees) which yielded a monotonic function from the melting point to the intersection temperature (indeed, to the critical point) was 180°C. Since there were four specific constraints, we chose a polynomial having four terms, thereby specifying each of the parameters, bi. The resulting equation is given in Table IV as Equation 11.
Discussion The results of the least-squares fit are given in Table IV. The estimated errors in each of the parameters are the changes in that parameter which will change 0 by one standard deviation, u.
Table IV. Equations for AIBr, Densityu For liquid: 92-319°C; vapor: 180-319°C D or d (g/cm3)= p e
+
f [{ - ( A + 87) + ((2 A + 8r)8r]”2] -k + 6 7 ) - [(2 A + 87)87]1’2)”a - A”’] (10)
007
(-(A
= (1.176=t0.001) X = 55 f 2 03 = -214 f 1 p o = 0.8622 f 0.0003 g/cm3 u = f0.0025 g/cm3 00
a2
For vapor: 97.5-180°C d = bo
+ b57 + b2.r’
b3.r3
bo = -2.5509 X
IO-* b l = 3.3803 X IO-‘ bi = -1.2122 X IO--‘ ba = 1.3176 X
aIn EquationlO,+terrnyieldsDand30
termyieldsd.
Journal of Chemical and Engineering Data, Vol. 19, No. 1, 1974
Together, Equations 10 and 11 yield the liquid densities with an estimated error of f0.1%, which compares well with previous results for AIBr3 ( 4 ) and with our results for AIC13 (5, 7). The vapor densities have an estimated error of f 6 % at the highest temperatures. This is about the same error as reported by Johnson et al. ( 4 ) at the same temperature region, which was the minimum temperature reached in their vapor density measurements. The error in vapor density increases, of course, as temperature falls. If the experimental liquid and vapor densities were to be plotted on Figure 1, which illustrates the entire coexistence curve for AIBr3, virtually all 726 points would fall within the thickness of the line (which is 2 u wide) used to portray Equations 10 and 11. The critical temperature has been reported variously as 490” ( 4 ) , 495’ (70),and 499°C (6). We used 490°C in our equations. Critical densities of 0.8605 f 0.0023 g/cm3 ( 4 ) and 0.8875 g/cm3 (70)have been reported. Even though our highest temperature investigated was approximately 170” below the critical point, we found a least-squares fit pc which lay within the estimated error limits of Johnson et al. ( 4 ) . Their value of ao, 1.1758 X also agrees with the present value of (1.176 f 0,001) X It should not be surprising, then, that Equations 10 and 11 can be used to find liquid and vapor densities over the entire liquid region up to the critical
500 450 400 U -*
5 2 e 5
350 300
W
250
IW
200 150
li
5
e
100 0.0
0.5
1.0 1.5 2.0 DENSITY, G/CM3
2.5
Figure 1. Coexistence curve for aluminum bromide
-, Calculated from Equations 10 and 11; 0 ,Biltz and Voight
(7); X, Zhuravlev ( 1 0 ) ; Johnson et al. ( 4 ) . Arrows indicate highest experimental temperature reached in present work
+.
temperature. Indeed, the experimental points observed by Johnson et al. lie slightly below Equation 10 at temperatures above our highest temperature. Similarly, 'Zhuravlev's liquid density data lie slightly above our Equation IO, also above our highest temperature. These data are shown in Figure 1. Safety
The same precautions should be taken as were reported previously (5) for the containment of liquids above their normal boiling points in glass vessels. Nomenclature
a j = empirical coefficients A = constant, a function of a2 and a3
bj = empirical coefficients B = constant, a function of a3 d = density of AIBr3 vapor D = density of AIBr3 liquid mi = mass of AIBr3 in ith tube n = number of individual experimental measurements Q = positive difference between rectilinear diameter and d or D Ti = total enclosed volume in ith tube t = temperature in degrees centigrade t, = critical temperature V i = liquid AlBr3 volume in ith tube zi '= residual; function to be treated by least-squares fitting p = overall tube average density; i.e., m / T p c = density at critical temperature p m = rectilinear diameter; i.e., ( d 0 ) / 2 u = standard deviation in Q 7 = distance from critical temperature, i.e., t, t q5 = fraction of total tube volume occupied by liquid; i.e., V I T
+
-
Literature Cited Biltz, W., Voight, A., Z. Anorg. Allgem. Chern., 126, 39 (1923). Boston, C. R., in "Advances in Molten Salt Chemistry," Chap. 3, J. Braunstein, G. Mamantov, and G. P. Smith, Eds., Plenum Press, New York, N.Y., 1971. Fischer, W., Rahlfs, O., Benze, B., Z. Anorg. Allgem. Chern., 205, 1 (1932). Johnson, J. W., Silva, W. J., Cubicciottl, D., J . Phys. Chern., 72, 1664 (1968). King, L. A., Seegmiller, D. W., J. Chern. Eng. Data, 16, 23 (1971). Rotinjanz, L., Suchodskl, W., Z. Phys. Chern., 87, 635 (1914). Seegmiller, D. W., Fannin, Jr., A. A., Olson, D. S.,King, L. A,, J. Chern. Eng. Data, 17, 295 (1972). Seegmiller, D. W., Rhodes, G. W., King, L. A,, lnorg. Nucl. Chern. Lett., 6, 885 (1970). "Selected Values of Chemical Thermodynamic Properties," Nat. Bur. Stand. Circular 500, p 731, 1952. Zhuravlev, D. I., Zh. Fiz. Khim., IO, 325 (1937). Received for review May 29, 1973. Accepted September 19, 1973
X-Ray Powder Data and Unit Cell Parameters of MgCI2.6H2O Charles A. Sorrelll and Roy R. Ramey Department of Ceramic Engineering, University of Missouri, Rolla, Mo. 65401
Detailed X-ray powder data for MgCIy6H20 were obtained by diffractometry by use of 'CuK, radiation at 22°C. The data were indexed on a bimolecular monoclinic unit cell, space group C2/m, with a = 9.858 0.001 A; b = 7.107 f 0.001 A; c = 6.069 f 0.001 A; 0 = 93" 47' f 10'. Calculated density was 1.591 g/cm3, compared with a measured density of 1.593 f 0.003 g/ cm3.
*
The structure of magnesium chloride hexahydrate, MgC12.6H20, was determined by Andress and Gundermann' ( I ) , who reported a bimolecular unit cell, space group C2/m, with a = 9.90 f 0.03 A; b = 7.15 f 0.03 A; c = 6.10 f 0.03 A; 0 = 94" f 20'. The only available X-ray powder data appeared in the original Hanawalt et al. compilation (3) and was subsequently included in the "Powder Diffraction File" ( 5 ) . Comparison of the struc-
' To whom correspondence should be addressed.
ture factors calculated by Andress and Gundermann with the powder data indexed by J. V. Smith indicates the incomplete nature of the powder. data. This, coupled with the relatively low precision. of the reported unit cell parameter measurements, prompted acquisition of the data reported in this work. X-Ray Procedures
Powder data were acquired- at 22°C by conventional methods by use of a General Electric XRD-700 recording diffractometer with CuK, radiation generated at 50 kVp and 20 Ma. Flat recessed sample holders machined from Lucite were used. Samples containing approximately 20% high-purity rock crystal quartz as an internal standard were scanned from 2" to 60" 2 6' at a rate of 0.2' per min, which permitted measurement of 2 0 values to the nearest 0.01 ". Samples containing no internal standard were then scanned, following alignment on the (020) line of the chloride, to provide complete interplanar spacing and intensity data. Journal of Chemical and Engineering Data, Vol. 19,No. 1, 1974
31
